Electrodes for electrolytic processes

ABSTRACT

This invention relates to electrolytic electroplating processes and devices. In accordance with the invention, the absorbent material that is conventionally used, for example, in the brush or tampon process, consists of an absorbent porous carbon material. A device for use in this context can comprise an electrode in contact with at least one carbon material member.

ite States atent lcxi et a1.

[451 Jan.25,19'72 ELECTRODES FOR ELECTROLYTIC PROCESSES Inventors: JeanJ. G. lcxi, Paris; Philippe J. Tilche,

Clamart, both of France Assignees: Dalic S.A., Paris, France; LeCarbone-Lorraine S.A., Paris, France Filed: Apr. 25, 1969 App1.No.:819,142

Foreign Application Priority Data Apr. 29, 1969 France ..149897 US. Cl...204/l5, 204/143 R, 204/143 M,

204/224, 204/271, 204/274, 204/284 Int. Cl. C23b 5/48, C23b 5/76 Fieldof Search... ..204/224, 271, 143 RM, 294,

References Cited UNITED STATES PATENTS 10/1967 Wolfer ..204/2243,471,383 10/1969 Tiedemann ..204/294 X 3,474,013 10/1969 lnoue..204/224 X FOREIGN PATENTS OR APPLICATIONS 18,643 8/1900 Great Britain493,108 9/1938 Great Britain...

39,320 1/1964 Japan ..204/224 Primary Examiner-John H. Mack AssistantExaminerD. R. Valentine Attorney-l-lolcombe, Wetheril1& Brisebois [57]ABSTRACT This invention relates to electrolytic electroplating processesand devices. In accordance with the invention, the absorbent materialthat is conventionally used, for example, in the brush or tamponprocess, consists of an absorbent porous carbon material. A device foruse in this context can comprise an electrode in contact with at leastone carbon material member.

7 Claims, 11 Drawing Figures PATENTEU meslsnz 3,637,468

SHEET 1 UF 3 PRIOR ART FIG 2 PRIOR ART mmumnummmu ljllllllll FIG3 F|G4ELECTRODES FOR ELECTROLYTIC PROCESSES Electrolytic processes using brushand tampon, etc., are well known and have important industrialapplications, not only in the fields of metal and metal-alloydepositions but also in the field of electrochemical treatments andapplications, such as for example: anodic oxidation, electrochemicalmachining and/or polishing, etc. The characteristics are much the samewhether the workpiece to be treated be the cathode or the anode. Theprocess consists essentially in moving an absorbent device, impregnatedwith an appropriate electrolyte, on the conductive workpiece to betreated.

It is an object of the invention to obtain a substantially uniformelectric field and to diminish the resistance of the absorbent material.It is also an object to be able to make the absorbent material as thinas possible.

To this end, the invention consists in an electrolytic process utilizinghighly absorbent porous carbon materials, particularly in thoseprocesses known as brush or tampon processes, and is applicable both toanodic systems, e.g., for the deposition of metals, and to cathodicsystems, e.g., for anodic oxidation, electrochemical machining andelectrolytic polishing.

The invention also consists in a device useful to carry out thisprocess, and comprising an electrode in contact with at least one carbonmaterial member. The member is preferably nonrigid and may be cementedto the electrode with organic substances followed or not by pyrolysis.Alternatively, the parts may be attached to one another by threads whichmay or may not be, carbon.

These devices may be used in contact with electrodes, to receiveelectrolytic feeding; to serve as devices for the circulation of afluid; to enable them to be heated by the same means or by an electriccurrent, or to be polarized in relation to the electrode. They may alsobe used in electrolysis by means of fused salts. In tank platingprocesses they may be used to change the behavior of soluble anodes orto establish an homogeneous electric field or to improve electrodes usedin electrochemical machining.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings which shown someembodiments thereof by way of example, and in which:

FIG. 1 shows a diagrammatic representation of the knownelectrodeposition of metals,

FIG. 2 schematically shows a known system of electrolytic plating withcooling,

FIG. 3 shows a first embodiment of a device according to the invention,

FIG. 4 shows how the distance between a pseudoanode and a cathode canremain constant,

FIG. 5 shows an anode with certain fittings,

FIG. 6 shows an insulating component,

FIG. 7 shows a means for the distribution of electrolytes,

FIG. 8 shows a device capable of receiving electrolysis of fused salts,

FIG. 9 shows a device comprising a protecting ring,

FIG. 10 shows a cross section along the line X-X of FIG. 9, and

FIG. 11 schematically shows how a substantially uniform electric fieldis obtained.

Referring now to the drawings, in the case of the knownelectrodeposition of metals, FIG. 1 shows an anode 1 in contact with anabsorbent material 2 that is rendered electrically conductive byimpregnating it with an appropriate electrolyte, the constituentmaterials of the tampon being preferably hydrophilous cotton-wool,cellulose, etc., or hydrophobic synthetic fabrics, brushes withnonconductive bristles, etc., or a combination of these. The whole ofthe anode l and the absorbent material 2 is contained in an electricallynonconductive head T. The anode 1 and a workpiece 3 to be plated formingthe cathode are, of course, connected to an electric power sourceschematically illustrated at G. This device may use either solubleanodes (e.g., copper in the case of electrodeposition of copper), oralternatively nonsoluble anodes.

The use of a high-current density necessary for industrial applicationsof the process requires a higher voltage than that used for conventionalbath plating which results in the production of heat by the Jouleeffect, and therefore often requires the cooling of the plating device.This is obtained either by an air-cooled metallic radiator 4 as shown inFIG. 1 or by the circulation of a fluid 5 (e.g., water) as shown in FIG.2. FIG. 2 represents schematically the plating of a rotating,cylindricalshaped workpiece component 3, a water jacket in which thecooling fluid 5 circulates being incorporated in the anode 1.

In order to obtain a uniform electric field and to diminish theelectrical resistance of the absorbent material 2 the thickness of thelatter is to be as thin as possible (see example in FIG. 2). Theabsorbent power of this material is therefore reduced and thecirculation of the electrolyte which occasionally is injected,consequently becomes more difficult.

The applicants have solved these difficulties by using self electricallyconductive absorbent materials described as porous material of amorphousor graphitized carbon obtained for instance by pyrogenation of organic(natural or synthetic) felts, fibers, cloth, etc.

FIG. 3 shows a device which illustrates in principle the object of thepresent invention. The anode 1 is put into contact with a porous carbonmaterial member C2 placed in between the anode l and the nonconductiveabsorbent material 2. These carbon materials (amorphous or graphitized)may absorb for example an amount of electrolyte equal to percent oftheir proper volume. Considering that their own electric conductivity isfar superior to that of the impregnating electrolyte, for example about90 percent of the current passing through the device may thus beconducted by this porous material. Consequently, one may use avoluminous absorbent material C2 and 2. The thickness of thenonconductive absorbent material 2 may be reduced since the carbonaceousmaterial C2 serves as an anode and is therefore in close contact withthe surface of the workpiece 3 to be treated. For this reason theelectric field is much more homogeneous, the coating more even, theJoule effect reduced, all of which represents an important advantage.

Moreover, this absorbent material is nonrigid and adaptable to anycomplex shaped profiles without requiring any specific machining of theanode 1; since the easily adaptable, conductive carbonaceous absorbentpart operates as an anode, the distance between this pseudoanode and thecathode remains constant (FIG. 4).

The intrinsic electrical conductivity of the material of the member C2makes it easy to provide the anode l with different fittings e.g.,perforated electrolyte tubes 6 made of insulating materials 7 as shownin FIG. 5; mechanically or otherwise deformable anodes, even by aninsulating component 8 as shown in FIG. 6, since the electric current isdistributed by the carbonaceous material C2 underneath this insulatorand therefore maintains a uniform electric field without any blanketingeffect.

These porous carbon materials are very suitable for the manufacture ofcomplicated assemblies. By the use of organic cements they may beattached together or to carbon or graphite supports or other materialswith a basic carbon content. The assemblies thus obtained maysubsequently be heat treated, i.e., pyrogenized or pyrolyzed as a resultof which an entirely carbonaceous matter is obtained.

This makes it possible to place tubes inside the absorbent material 2 toprovide for the circulation of heating or cooling fluids 9 and for thedistribution of the electrolytes 10 as shown in FIG. 7 where theabsorbent material is made of two graphite plates 11 fixed to a porouscarbonaceous material C21 and to another porous carbonaceous materialC22-the whole assembly being contained in an electrode 1 support Wallowing at C21 the distribution of a fluid with thermal action and atC22 electrolyte distribution-and of a nonconductive porous material 12e.g., asbestos.

The chemical inertia of the absorbent carbon materials allows for theuse of electrolytes such as those containing concentrated sulphuric orphosphoric base acid which normally cannot be used with nonpyrolyzedabsorbent organic materials.

The device of FIG. 7 can be adapted for electrolytic polishing, theworkpiece 3 becoming the anode and the electrode 1 becoming the cathode.

These carbon materials are not destroyed by high temperatures, and arethus suitable for use in a device capable of receiving electrolysis offused salts as shown in FIG. 8 where a high temperature supplied by alow-voltage AC current G2 is transmitted via a rheostat Rh, to the anode1 and a carbon ring C2 insulated from the workpiece 3 cathode and theanode 1.

They can further be used to change the current distribution byappropriate polarization. The diagram of FIG. 9 shows a devicecomprising a protecting ring C23. This ring is made ofa graphite tube 14fixed and pyrogenated onto a ring C23 of porous carbon material and issubsequently polarized in relation to the anode l by an auxiliary powersource GA for example. The protecting ring is insulated by an insulatingliner 15 from the porous absorbent material C2 in contact with the anode1 and is placed inside the noncarbonaceous absorbent mass 2. FIG. 10shows a cross section along the line X-X of FIG. 9 of the differentcomponents of this protecting ring C23.

Insoluble anodes are often sensitive to electrolytic reaction and aresubject to wear in the long run. The use of conductive absorbentmaterial acting more or less as an anode as shown in FIG. 3 protects theinsoluble anodes from this type of wear. An accidental short circuitbetween the carbonaceous material and the workpiece is temporary andwithout danger since the contact, being perfectly wet, prevents suddencurrent rises.

In the case ofa soluble anode clad with the material forming the subjectof the present invention, the material reduces the dissolution of theanode, for example: with an appropriate thickness of the carbonaceousmaterial the rate of dissolution of the anode may be kept equal to therate of deposition on the cathode in case the latter is inferior to theformer. For conventional plating applications in tanks, anodes clad withone of these materials that may also serve as a filter for the residuesfrom the anode dissolution, maintain the stability of the bath platingsolutions. In placing the porous carbon material 17 close to the cathode16 a uniform electric field is achieved and provided that its thicknessis small the material does not act as an intermediate electrode sincedue to its porous texture any metallic deposit is avoided as shown inFIG. 11.

This is the same in the case of electrochemical treatments in tankswhere the workpieces to be treated become anodes such as for example inelectrochemical polishing, etc. The cathodes may thus be protectedagainst electrolytic attacks, etc.

Particularly in the case of electrochemical machining without a tampon,cathodes modified according to the present invention represent aconsiderable advantage. As is well known, electrochemical machiningconsists essentially in an electrolytic attack of the anodic part with asuitable electrolyte by means of an insoluble cathode having a shapesimilar to that of the part to be machined. For this purpose, a verysmall gap between anode and cathode (approx. 20/100 mm. in most cases)is absolutely necessary to ensure an electric field as uniform aspossible and to allow the highest current densities, a rapidly flowingelectrolyte being passed into the gap. Since the cross section of theelectrolyte flow is very small, the electrolyte must be injected underhigh pressure requiring strong supports able to resist heavy mechanicalstresses and to ensure a precise positioning of the anode and cathode.

The applicants have found that a cathode clad with a porous amorphous orgraphitized carbon material, due to its permeability during theelectrolyte flow (e.g., 90 percent of its proper volume) makes itpossible to increase considerably the speed of the electrolyte flow(e.g., 200 times) and to reduce in an even greater proportion thepressure required for the electrolyte circulation while stillmaintaining a very small gap owing to the fact that the porous carbonmaterial acts partially or totally as an electrode due to its very highelectric conduc tivity. Consequently, it is easier to provide thesupports and it is even possible to operate in open tanks as used forconventional electrolytic treatments, thus reducing the danger ofexplosive gas mixtures, the detrimental rise or variation oftemperature, the danger of accidental short circuits, etc.

The manufacture of these improved cathodes is carried out as describedabove for other types of electrodes by assembling, forming, cementingsometimes followed by pyrolysis, etc., to obtain the desired shapes. Thevery small gap between the porous carbon material and the workpiece tobe treated plays the part of the nonconductive porous material holdingthe electrolyte in the processes known as brush or tampon platingprocesses.

It will be understood that the devices shown in FIGS. 5, 6, 7 and 9 arealso applicable for electrodes used for electrochemical machiningwithout tampons as well as for other electrochemical treatments in tankswhere such type of electrodes provide a solution to the high currentdensity conditions and forced electrolyte circulation.

The following indicative, but not restrictive examples will ensurebetter understanding of the advantages of the present invention.

EXAMPLE I A prior art device such as that shown in FIG. 1 with a certainelectrolyte solution gives the following characteristics:

200 A./dm.

voltage under load current density with a thickness of 12 mm. for anonconductive tampon.

The same device, modified as shown in FIG. 3 which is one of theembodiments of the present invention with the same electrolyte solution,the tampon being made of a 3 mm. nonconductive material 2 and a 9 mm.amorphous carbon felt C2 leads to the following new conditions:

voltage under load 10 v. current density 200 AJdm. Joule effect reducedby 40% EXAMPLE II EXAMPLE III With a device as shown in FIG. 2 for thecoating of an aluminum piston 500 mm. in diameter, 600 mm. in length andof an average thickness of 25 mm., the current passing through thenonconductive tampon 2 and the piston 3 has to be kept down to 300 a.because of the danger of overheating due to the flow of current. If ahigher current density is applied the plating has no longer the requiredphysical properties, and might not adhere to the base metal owing to thelatters expan- SlOIl.

The introduction of a system such as shown in FIG. 7

thickness of C21 thickness of C22 l7 mm.

EXAMPLE IV Using a device as shown in FIG. 1 the anodic oxidation ofaluminum with a sulphuric acid solution 200 g./ 1. at 12 v. has becomepossible by replacing the nonconductive absorbent 2 with a chemicallyinert tampon made of:

17 mm. of graphitized carbon absorbent C2 1 mm. of P.T.F.E. fine-meshfabric (0.07 mm. thread) according to the principle shown in FIG. 3except. that the polarities are reversed.

We claim:

1. A process for the electrolytic treatment of a conductive workpiece,wherein said workpiece is held in contact with one face of a constantthickness layer of a nonconductive absorbent material, the opposite faceof said layer is held in contact with one face of a layer of highlyabsorbent flexible electrically conductive material of fibrous porouscarbon permanently filled with electrolyte, the opposite face of saidcarbon layer is held in contact with a conductive electrode element, theworkpiece is connected to one pole of an electrical power source, andthe electrode element is connected to the other pole of said powersource.

2. An electrode assembly for the electrolytic treatment of a conductiveworkpiece comprising an electrode layer element connectable to oneterminal of an electrical power source, an electrically conductive layerof a highly absorbent flexible fibrous carbon in contact with saidelectrode layer, and a layer of porous nonconductive material in contactover one face thereof with said carbon layer and adapted, whileremaining of constant thickness, to be held with its opposite face incontact with the workpiece which is to be treated and which isconnectable to the other terminal of said power source.

3. An electrode assembly according to claim 2, wherein the electrode isprovided with perforated tubes of insulating material for transportingthe electrolyte.

4. An electrode assembly according to claim 2, wherein the absorbentcarbon layer is provided with tubes for the circulation of heat exchangefluid and for the distribution of electrolyte.

5. An electrode assembly according to claim 2, wherein the carbon layeris mainly graphitized carbon.

6. An electrode assembly as claimed in claim 2, wherein the assembly iscemented together with organic cements.

7. An electrode assembly as claimed in claim 6, wherein the cementedassembly is pyrolyzed with carbonaceous electrodes.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTWN Patent No. 1 375Dated January 25, 1972 JEAN J G ICXI and PHILIPPE J TILCHE Inventor(s) 7It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

[30] Foreigh Application Priority Data April 29, 1968 France 1 49897(SEAL) Attest:

EDWARD M.FLETCHER,JR.

ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM P0 1050(10-69) USCOMM-DC 50376-P69 U.54 GOVERNMENT PRINTING OFFICE I 1969O'36G-334

2. An electrode assembly for the electrolytic treatment of a conductiveworkpiece comprising an electrode layer element connectable to oneterminal of an electrical power source, an electrically conductive layerof a highly absorbent flexible fibrous carbon in contact with saidelectrode layer, and a layer of porous nonconductive material in contactover one face thereof with said carbon layer and adapted, whileremaining of constant thickness, to be held with its opposite face incontact with the workpiece which is to be treated and which isconnectable to the other terminal of said power source.
 3. An electrodeassembly according to claim 2, wherein the electrode is provided withperforated tubes of insulating material for transporting theelectrolyte.
 4. An electrode assembly according to claim 2, wherein theabsorbent carbon layer is provided with tubes for the circulation ofheat exchange fluid and for the distribution of electrolyte.
 5. Anelectrode assembly according to claim 2, wherein the carbon layer ismainly graphitized carbon.
 6. An electrode assembly as claimed in claim2, wherein the assembly is cemented together with organic cements.
 7. Anelectrode assembly as claimed in claim 6, wherein the cemented assemblyis pyrolyzed with carbonaceous electrodes.